Reclaiming scrap of natural rubber mixed with buna-s



Patented May 31, 1949 RECLAIMING sonar or NATURAL RUBBER mxsn wrrn BUNA-S Robert L. Randall, St. Louis, Mo., assignor, by

mesne assignments, to Midwest Rubber Beclaiming Company, East St. Louis, 111., a corporation of Delaware Application July 14, 1945, erlal No. 605,183

'1 Claims. (01. 260-) No Drawings.

The present invention has as its object the perfection of a process for reclaiming waste rubber scrap, and particularly old automobile and truck tires, and to a practical and commercial process for making the rubber content thereof available for re-use.

The process herein disclosed deals specifically with the reclaiming of stocks in which natural rubber is intermingled with the Buna-S rubber also known as GRS.

While commercial and practical methods of reclaiming rubber tire scrap and other rubber scrap which contain natural rubbers are well Mom and while more or less success has been achieved in reclaiming tires and other articles made of various synthetic rubbers, a very real problem has been presented to the industry in the reclaiming of stocks such as tire scrap which contain both natural and synthetic rubbers, particularly what is known as Buna-S or GRS, as the reactions of these materials in the reclaiming processes are quite distinct. This is mainl due to the fact that processes which will soften the Buna-S to the requisite degree render the natural rubbers too soft and mushy to make asatisfactory reclaim with an acceptable plasticity and other properties. Conversely, processes which soften the natural rubber to the proper degree will leave the Buna-S hard and unworkable. As a consequence, if the reclaimer employs a process which gives a commercially satisfactory reclaimed natural rubber, the losses and tailings due to the unreclaimed Buna-S particles result in excessive waste.

It is uneconomical to attempt to separate the component parts of tires which are made of combination of Buna-S and natural rubbers, although.

I loss due to tailings and rejects. The process. has

the great advantage that it may be carried on process.

with the usual factory routine and technique and except for the substitution of the reagents specifled herein for ordinary reagents, the new process requires no appreciable change in factory practices.

The synthetic rubber which has been almost universally employed in tires since Pearl Harbor is what is known as GRS or Buna-S rubber. This is a copolymer of butadiene and styrene and is used in certain tires as the only rubber-like component. In other tires the Buna-S rubber is used in the tread, .while the carcass contains natural rubber. In certain cases also natural rubber has been milled with the Buna-S rubber. This makes the perfection of a process which will reclaim any combination of both types of rubbers in varying proportions a valuable advance in this art. The problem is further complicated by the fact that it is impossible to determine the percentage of the two rubbers which may be present in batches of tires which are to be put through the reclaiming It is quite likely that these conditions will confront the tire reclaimer for a long period.

In evaluating the reclaimvarious tests are more or less standard, but the generally accepted standard is what is known as the Mooney plasticity test (see Industrial and Engineering Chemistry, Vol.6, p. 147, 1934). This method of testing plasticity is well known to those skilled in the art and is a fair method of determining this important characteristic of the finished product. Reclaims obtained by the process, disclosed herein from a great variety of scrap rubber containing both natural and Buna-S-rubbers have shown Mooney values ranging from over 30 to under and any finished product coming within this range is a satisfactory reclaim and may be employed with excellent results in subsequent manufacturing operations. 'It will be apparent that a reclaim made from mixed stocks by this process may be held to much closer Mooney ranges than with previously known processes.

A further advantage of the process is the fact, that much lower percentages of tailings are obtained. Tailings are the small particles of unreclaimed stock which detach themselves from the sheet of'reclaim as it is made on the refiner. It is desirable to maintain a tailing production of under 6%. As indicated herein, the tailings resulting from the use of this process willrun becontaining a wide variety of the two types of rubber discussed herein. The tires are then cut up and ground until-all of the particles thereof will 4 thenic (cyclo-parafllnes) and some cyclo-oleflnic compounds. The unsaturation of these compounds is found partly in the ring structures, and partly in the aliphatic side-chains. The aliphatic side-chains consist. of carbon and hydrogen only and usually do not contain more thanthree to four carbon atoms. In short this material can be defined as a mixture of compounds containing biand tri-cyclic fused ring structures with short pass through a %"mesh, the said particles'conaliphatic side-chains. The material has a very sisting of both rubber and fabric, cotton, rayon or high iodine number, being in the range between the like. This ground scrap can then be defibered 150 and 375 which is indicative of a high degree by mechanical means or by any well known chemof unsaturation. It is ordinarily a thick, dark ical process. Or, if desired, the defiberization brown, viscous liquid sold by a number of petromay be carried on simultaneously with the re-' leum refining companies and has a limited comclaiming process. In any case the rubber scrap is merclal value. Ananalysis of a typical oil of this fed to a jacketed digester oran autoclave where ty is a foll ws; i it is thoroughly agitated with a relatively large body of water and the selected reagents which act g fi g zg g" ga "aggggigf to to soften or "reclaim the rubber. This digestg 170 was, ing process is carried on for a number of hours Iodine 55; f 150450- until the reclaiming agents have fully acted upon N n 1 m 6045 the rubber. The digester is then emptied, the e cen liquid contents removed by mechanical means (2) The second reagent referred to above is well known and the reclaimed scrap is then essentially abietic acid and its equivalents. The washed to remove any traces of the free reagents. commercial form of abietic acid which is used The scrap is then milled and refined, the latter in the process is a yellow crystalline powder. process consisting in sheeting out the reclaim into i For the purpose of this application, this second very thin sheets. which are wound up on a roll reagent may be referred to as abietic acid, alfrom which the stock is cut when the batch has though such expression when used herein is inbeen completely refined. It is during this retended to include both commercial abietic acid fining process that the bits of unreclaimed ruband chemically pure abietic acid. This material her which constitute the tailings drop from the I is sometimes referred to as sylvic acid. It is not sheet. intended to exclude closely related diterpene car- During these latter operations, any fillingboxylic acids which have analogous molecular agents, softeners, mineral rubbers or reagents structures, such, for example, as abietinic acid, may be added as called for by the customer's specpimaric acid, sapinic acid and isomers of abietic ifications. The resultant product is a uniform acid. mass of reclaimed rubber of the proper plasticity It being understood that as it ispractically imand free of particles of unreclaimed rubber, or 40 possible to determine the exact ratio of natural pimples" as they are known in the trade. and Buna-S rubber which is in a batch, the exact In order to secure the results set forth, two proportions of the reclaiming resin'and abietic new reclaiming agents are employed in combinaacid or its equivalent cannot be fixed, but it is tion, and while their action may not be capable the intention to supply such proportions of the of positive ascertainment, it has been found that two reagents that will react properly with batches they work exceptionally well in the reclaiming containing wide variations of natural and synof mixed rubber scraps containing natural rubthetic rubber to produce an end product in which her and what has been defined as Buna-S or GRS both types of rubber have like or substantially rubber. The combination of reagents softens equivalent plastic properties. This factor may, each component part of the mix satisfactorily. therefore, be determined by experimentation, but In the absence of the treatment specified, the it has been the experience that the relative procrude rubber would be so soft and mushy as to portions of the abietic acid and the reclaiming make the whole batch unsuitable for the subseresin will be advantageously modified with the quent processing operations and for any useful varying proportions of natural and Buna-S scrap purpose thereafter. in the batch. As the percentage of natural rub- The two reagents employed are: ber increases, the proportion of abietic acid should (1) The oil-like residue obtained as a bybe'increased. product of gasoline refining by the clay tower The following illustrative examples are given, adsorption process or what is known as the "Gray not with the intent of limiting the invention to Tower process of gasoline refining, which is 00 the exact amounts. Proportions or temperatures, described in Burk, Thompson, Weith and Wilbut merely to give actual operative formulas liams, Polymerization, pp. 232-233. This oil-like which have given outstanding results in the recresidue is a mixture of unsaturated hydrocarbons lamation of mixed Buna-S and natural rubber with short aliphatic side-chains. These hydroscrap. In actual commercial practice these figcarbons consist of some aromatic, some naphures have been found to give excellent results:

Batch #1 Batch #2 Batch #3 gfi fifiittitii fiitar i%"3e::::::: i%%:::::: i tfifii." wa 4000parts parts 4.000 parts.

assesa zsa a Cookatlilii'O -I Sm-snu 9h 9 338;. Mooney Plasticity 64 82. Tailings 3% Nona 2%,

It will be observedthat the Mooney plasticity is excellent and characteristic of the highest grade of reclaim;

The above examples were given for a standard aqueous digesting method, but the same reagents may be employed in the steam digesting process where the ground mixed scraps are treated in the presence of the two reclaimingagents in a steam. heater and subjected to live steam at a predeter- 1 Batch #4 was a mixed gum stock; #5 a miscellaneous mechanical goods scrap; and #6 a clicker block and gasket mixed scrap.

All six of the above batches treated in the 4 manner described gave reclaims which are capable of being vulcanized into useful products having satisfactory physicalproperties.

It is oftentimes impossible, due to various causes, to determine the proportions of natural rubber and Buna-S in a commercial lot of scrap. The following is an actual example of the process as it has been successfully applied to mixtures; I of scrap containing both materials, but in unknown and undeterminable proportions.

Batch #7 Ground whole tire scrap containing both natural rubber andv Buna-S in unknown proper-- tions 5,000 lbs. Water 9,110 lbs. Reclaiming resin 1'7 or 850 lbs. Abietic acid 3% or 150 lbs. Heat at 190 lbs. pressure in. a

digester 12 /2 hrs. Mooney plasticity 72 Tailings None The temperatures and times at which the reaction is carried out whether in a digester, potheater. or autoclave may be varied widely, but it will be understood that during the process the scrap is in contact with steam and that in general the higher the temperature the shorter the time required, and vice versa. v

It will be seen that the process described herein has very substantial value in the rubber reclaiming industry and permits it to cope successfully with the problems which are presented by present day conditions in which the reclaimer finds him-.

self with large stocks of tires and other used rubber articles which may contain wide variations in the proportions of the different types of rubbers contained therein. These G problems have been created by the use of Buna-S in combination with natural rubbers, the scrap of which come to the reclaimer without any attempt at segregation with respect to the rubber constituents.

It may be stated that the resin reclaiming agent, i. e., the by-product of the Gray process of gasoline refining, has been found to possess very superior properties when used by itself in the reclaiming of natural rubber and synthetic the joint presence of both types of rubber in a" single-stock. It is particularly valuable in the reclaiming of the butyl type synthetic rubbers and straight Buna-S rubber. This discovery is a very valuable one and is made the subject of my copending application Serial No. 631,481, filed Nov. 28, 1945. It is not intended to be dedicated hereby. I

In conclusion it may be stated that the specific details of the process as disclosed herein are not intended-to be construed-as limiting the invention beyond the apparent scope of the claims. The process may be modified or improved upon without departing from'the principles of the invention. It has been sought herein to give a full and adequate disclosure of the best known or preferred forms of the invention, and this disclosure is not to be considered in any other aspect.

What is claimed is: i

1. The process-of reclaiming mixed, previously vulcanized rubber scrap containing both natural rubber and an elastomer which is a rubbery copolymer of butadiene and styrene, comprising heating the said scrap with from 1 to 15% of abietic acid and from 3 to 30% of Gray Tower resin oil which is a residual by-product obtained in the refining of gasoline.

2. The process of reclaiming mixed, previously vulcanized rubber scrap containing both natural rubber and a synthetic rubber made by the copolymerization of butadiene and styrene, comprising heating said scrap in the presence of not in excess of 15% of abietic acid and not in excess of 30% of Gray Tower resin oil which is a Specific gravity .94 to .97

Boiling range (before decomposition) "C 170 to 350 Iodine val a 150-250 Nonevolatile per cent" 60-85 3. The process of reclaiming mixed, previously vulcanized rubber scrap containing both natural rubber and an elastomer which is a rubbery copolymer of butadiene and styrene, which com- .priscs heat treating. said scrap in the presence product obtained in refining gasoline.

4. In a process of reclaiming rubber scrap which contains natural rubber and an elastomer which is a rubbery copolymer of butadiene and styrene, the steps of adding to said scrap not in excess of 15% of at least one diterpene carboxylic acid selected from the group consisting of abietic acid and resin acids which are isomers of abietic acid and not in excess of 30% of Gray Tower resin oil which is a residual by-product obtained in refining gasoline,-.and heat treating the mixture until both types of rubbers are rendered plastic to the degree that the product has a Mooney value between 30 and 100.

5. The process of reclaiming scrap containing natural rubber and an elastomer which is a rub bery copolymer of butadiene and styrene which comprises heating the scrap in comminuted condition in the presence of steam, not in excess .of 30% of Gray Tower resin oil which is a byproduct obtained in the refining of gasoline and rubber where the problem is not complicated by 76 not in excess of 15% of abietic acid.

of 15% of at least one diterpene carboxylic acid, selected from the group consisting of abietlc acid and resin acids which are isomers of abietic acid,

and not in excess cit 30% of Gray Tower resin oil which is a ay-product obtained in the refining of gasoline. v

7. The process of reclaiming scrap containing natural rubber and an elastomer which is a rubbery copoiymer of butadiene and styrene which comprises heating the scrap incomrninuted con- 5 2,423,033

of abietic acid and from 3 to 30% of Gray Tower resin oil which is a by-product obtained' in the refining of gasoline. I

1 ROBERT L. RANDAIL.

'RErmnNcEs crrnn The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,008,102 Hyman July 16, 1935 2,324,980 Kilbourne July 20, 1943 Le Beau June 24, 1947 dltion in the presence of steam, from 1 to 15% v 

